Defconfig tweak and Makefile optimization
ARM: use generic strnlen_user and strncpy_from_user functions

    This patch implements the word-at-a-time interface for ARM using the
    same algorithm as x86. Although we have a clz instruction from ARMv5,
    this only saves us one mov instruction when building with Thumb-2 and
    makes no difference when targetting ARM, so we use the magic 0x0ff0001
    constant for all CPUs. For big-endian configurations, we use the
    implementation from asm-generic.

    With this implemented, we can replace our byte-at-a-time strnlen_user
    and strncpy_from_user functions with the optimised generic versions.